<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .button {
      width: 400px;
      height: 60px;
      border-radius: 100px;
      background-color: #99e9f2;
      color: #fff;
      text-align: center;
      line-height: 60px;
      font-size: 30px;
      margin: 50px auto;
      transition: all .1s;
    }
    .button:hover {
      transform: scale(1.2);
    }
    .fixed {
      position: fixed;
      top: 50%;
      left: 50%;
      width: 300px;
      height: 100px;
      background-color: rgba(0, 0, 0, .5);
      font-size: 14px;
      display: flex;
      justify-content: center;
      align-items: center;
      color: #fff;
      transform: translate(-50%, -50%);
    }
  </style>

</head>

<body>
  <div class="button">
    点击按钮
    <div class="fixed">这是一个弹窗</div>
  </div>
</body>

</html>